A turbocharger includes a compressor and a turbine. The turbine drives the compressor with exhaust energy created by the internal combustion engine. The engine exhaust drives a turbine wheel in the turbine of the turbocharger and is discharged through an exhaust system. The turbine wheel drives a shaft connected to a compressor wheel in the compressor which pressurizes intake air, previously at atmospheric pressure, and forces it typically through an intercooler and over a throttle valve and into an engine intake manifold. Controlling the output of the turbocharger to obtain desired engine operation has been a long standing problem. Too much output can create erratic engine performance and permanently damage engine components. Too little output causes engine hesitation and loss of power. Additionally, changes in atmospheric pressure, ambient temperature and engine speed affect the overall efficiency of the turbocharger which directly affects the performance, power output, and fuel economy of the engine.
Prior to the invention of the noted U.S. Pat. No. 5,551,236, hereinafter the '236 patent, some turbocharger systems used a bypass valve connected to the output of the compressor to relieve excessive pressure. Typically, the bypass valve of these prior art systems sensed the differential pressure between the compressor discharge and intake manifold, i.e. the pressure difference across the throttle valve, and opened the bypass valve to vent pressure at a given threshold and remained open until the pressure fell below the threshold level. Other systems used a wastegate between the exhaust manifold discharge and the exhaust system to regulate the turbocharger by diverting engine exhaust energy from the turbine. The wastegate of this prior system was actuated by a compressor discharge pressure sensing type valve. Because these systems operated independently, and both were either opened or closed depending on the compressor discharge pressure, the turbocharger had a very limited range of operation. The range was so limited that it was necessary to use different turbocharger hardware, i.e. turbine and compressor wheels, for varying attitudes of operation and engine configurations.
Since the turbocharger's compressor and turbine wheels are sized not only for altitude, but also to achieve a rated power horsepower at a desired speed for each particular engine, the power and torque output of an engine would drop dramatically when the engine is run at less than the rated speed or at a different altitude because the pressure sensing valves were only dependent on compressor discharge pressure and would actuate regardless of engine speed. For example, an engine rated at 190 psi BMEP (braking mean effective pressure) at 1,000 rpm, would have trouble producing 190 psi BMEP at 700 rpm because of the reduced output of the turbocharger due to the falling speed and because of the mechanical pressure sensing and releasing valves previously used.
Typically, large industrial internal combustion engines operate for long periods and are capable of generating thousands of horsepower. These engines are designed to operate at 10% over rated load intermittently, and are used for generating electrical power, pumping natural gas and oil powering large ships and off-shore well drilling operations, and so on. In such applications, it is desirable to produce maximum power and/or maintain maximum torque at reduced engine speeds. However, because previous turbocharger control systems were simply a function of the compressor discharge pressure, the mechanical valves would release pressure regardless of the engine's speed and therefore regardless of the engine's need. Under such circumstances, when the engine speed is reduced but the load is maintained, the engine requires near constant intake manifold pressure to maintain torque output. Under these conditions, it would be desirable to adjust the bypass valve to change total mass airflow and adjust the wastegate to direct more engine exhaust to the turbocharger in order to produce near constant intake manifold pressure such that the compressor operates more efficiently at these speed and load conditions.
The invention of the '236 patent provides a simple and effective method and system for maintaining engine torque output at lower than rated speeds and at varying ambient temperatures and barometric pressures by stabilizing the turbocharger output within a predetermined range of efficient operation. The invention of the '236 patent provides an electronic turbocharger control system, including a wastegate and bypass valve, which eliminates the need for matching individual compressor and turbine wheels of a turbocharger for each particular engine configuration and application. This particular aspect of the invention of the '236 patent allows a manufacturer to use one set of turbocharger hardware for various engine applications. For example, prior to the invention of the '236 patent, as many as 13 different turbocharger wheels would be required to adequately cover a 0-7,000 foot above sea level range of elevations. With the invention of the '236 patent, one set of turbocharger hardware can be used at all elevations in this desired range. Further economic advantage is gained not only by the low cost of the electronic control relative to the high cost of the compressor and turbine wheels, but also by the elimination of inventory and the need for custom wheels for special applications. Customer satisfaction may also be greatly improved by the elimination of long procurement leadtimes for replacement components. The invention of the '236 patent provides constant torque at varying engine speeds allowing an operator to obtain additional load at reduced engine speed for improved fuel economy. The invention of the '236 patent provides maximum power over a range of engine speeds while maintaining the turbocharger in its most efficient range of operation. The invention of the '236 patent provides a control system which maintains turbocharger efficiency within a desired range of pressure ratio versus mass air-flow rates.
The invention of the noted U.S. Pat. No. 5,816,047, hereinafter the '047 patent, relates to an electronically controlled wastegate valve on a turbocharged internal combustion engine. In particular, the invention of the '047 patent relates to a control system and method that adaptively adjusts the throttle pressure reserve to improve load acceptance when the load on the engine is fluctuating, and optimize engine efficiency when the load on the engine is relatively steady. The invention of the '047 patent is primarily directed to large industrial internal combustion engines that are fueled by natural gas, and are intended to operate for long periods, and are capable of generating thousands of horsepower. These large engines are typically used for generating, electrical power, pumping natural gas and oil, or powering offshore well drilling operations, and so on.
The invention of the '047 patent applies to turbocharged internal combustion engines having a wastegate valve. A turbocharger includes a turbine and a compressor. In a turbocharged engine, exhaust drives a turbine wheel in the turbine, which in turn drives a shaft connected to a compressor wheel in the compressor. The exhaust exiting the turbocharger discharges through an exhaust outlet duct. The compressor typically pressurizes or turbocharges ambient air, and forces the pressurized intake air through an intercooler and a carburetor (or other fuel addition device such as electronic fuel injection), past a throttle valve, and into an engine intake manifold. In some systems, the carburetor is located upstream of the compressor so the compressor pressurizes a mixture of fuel and air. Exhaust discharges from the engine through an engine exhaust manifold, and is directed through an exhaust manifold discharge duct to the turbine of the turbocharger. A wastegate valve is often provided to divert some or all of the engine exhaust energy away from the turbine of the turbocharger. Usually, the wastegate valve is located within a passage between the exhaust manifold discharge duct and the exhaust system outlet duct.
Using a standard wastegate control otherwise known as a maximum boost regulator, the wastegate valve remains closed until the pressure of the pressurized intake air from the compressor becomes large enough to actuate a spring mechanism in the wastegate actuator to open the wastegate valve. The system thus diverts engine exhaust away from the turbine in the turbocharger when the compressor discharge pressure reaches a maximum boost value. In such a maximum boost system, the wastegate valve remains closed at light loads and continues to remain closed until the engine reaches about 80% to 90% of full load. Even when the throttle is fully open in a maximum boost system, opening the wastegate valve will reduce the amount of energy supplied to the turbine in the turbocharger, and in turn will maintain the compressor discharge pressure at the maximum boost value.
It is known in the art to use a fixed .DELTA.P wastegate control in conjunction with a maximum boost regulator. In a fixed .DELTA.P wastegate control, the wastegate valve is adjusted to maintain a fixed pressure reserve across a throttle (i.e. a fixed pressure drop across the throttle at light or medium engine loads). Compared to the standard wastegate control using only a maximum boost regulator, the fixed .DELTA.P wastegate control tends to improve engine efficiency at light and medium loads due to reduced exhaust pressure and the associated pumping losses. The maximum boost regulator in a fixed .DELTA.P wastegate control operates in a similar manner to the standard wastegate control to limit the maximum compressor discharge pressure. In a fixed .DELTA.P wastegate control, the throttle pressure reserve can be monitored mechanically using a pressure tap upstream of the throttle and another pressure tap downstream of the throttle. The pressure difference between the pressure taps typically drives a spring actuated wastegate valve actuator. Alternatively, the throttle pressure reserve can be determined electronically by sensing the pressure both upstream and downstream of the throttle, and subtracting the two sensed pressures electronically to determine a pressure difference across the throttle.
Large industrial internal combustion engines typically operate at a fixed speed, but the load on the engine varies. If there is a large increase in the load, the throttle on the engine opens and the pressure difference across the throttle drops, which provides an initial increase in engine power output. In other words, the throttle pressure reserve provides the initial increase in engine power output. The remaining increase in power output is due to the fact that the turbocharger will continually speed up as the wastegate remains closed. The wastegate will remain closed until the throttle pressure reserve (i.e. the pressure drop across the throttle) recovers. It takes a relatively long time (e.g. 5 seconds) for the turbocharger to speed up and for the pressure drop across the throttle to recover completely. In large industrial internal combustion engines having a fixed .DELTA.P wastegate control, the desired throttle pressure reserve is normally chosen to compromise between reasonable fuel consumption and yet maintaining satisfactory load acceptance.
With a fixed .DELTA.P wastegate control, engine efficiency can be improved by maintaining a low pressure drop across the throttle, but the load acceptance of the engine is reduced. A higher throttle pressure reserve permits the engine to accept greater loads at constant speed or to accelerate a constant load upon the opening of the throttle without hesitation due to the lack of intake manifold pressure. However, to obtain optimum engine efficiency, it is desired to maintain the throttle in an open position thus reducing the throttle pressure reserve and the load acceptance of the engine. There is therefore a trade-off between engine response and fuel consumption.
It can be appreciated that it would be desirable to maintain a relatively small throttle pressure reserve to improve engine efficiency when the load on the engine is relatively stable, yet maintain a relatively large throttle pressure reserve to improve engine load acceptance when the load on the engine fluctuates. The invention of the '047 patent provides an adaptive wastegate control in which the desired throttle pressure reserve, or .DELTA.P set point, is determined depending upon the history of the engine load, or the history of some other factor such as engine speed or intake manifold absolute pressure which can give an indication of engine load. In this manner, the invention of the '047 patent provides a large throttle pressure reserve when the engine load is fluctuating, thus improving the engine response to load changes, and a smaller throttle pressure reserve when the engine load is relatively stable, thus improving fuel consumption.
In particular, the preferred embodiment of the invention of the '047 patent involves the use of an electronic controller that receives a signal from a pressure transducer located upstream of the throttle, a signal from another pressure transducer located downstream of the throttle, and an engine load signal from an engine load sensor. The electronic controller generates a wastegate control signal that instructs a wastegate actuator to close or to open the wastegate valve. The electronic controller adaptively generates a desired throttle pressure reserve value that depends at least in part upon the prior history of the engine load. If the pressure drop across the throttle, as determined from signals from the upstream and downstream pressure transducer, is greater than the desired throttle pressure reserve value, the electronic controller generates a wastegate control signal instructing the wastegate valve to open. If the pressure drop across the throttle is less than the desired throttle pressure reserve value, the electronic controller instructs the wastegate actuator to close the wastegate valve. Since the desired throttle pressure reserve value depends at least in part on the history of the engine load, the electronic controller can provide a relatively large throttle pressure reserve for fluctuating loads to improve load acceptance, and cam provide a relatively low throttle pressure reserve to improve fuel consumption when the loads are relatively steady.
The desired throttle pressure reserve value in the '047 patent is consistently driven downward, thus improving engine efficiency or fuel consumption absent a significant fluctuation in the engine load to drive the desired pressure reserve value upward. This can be accomplished in the electronic controller by applying a constant negative gain term, as well as engine load terms, in a loop update scheme. It is not necessary that this type of adaptive scheme be used over all ranges of engine load. For instance, in industrial electrical power applications, engine efficiency at light engine loads is relatively unimportant, so it may be desirable to set the throttle pressure reserve at a high level for light loads, and use an adaptive scheme to improve engine efficiency at higher loads only.
Engine load can be monitored in several ways. One practical way for monitoring change in engine load is to monitor engine speed such as with an engine rpm sensor. Engine speed change is a fairly good surrogate for engine load change especially in large industrial applications. The invention of the '047 patent achieves its primary objective of allowing large industrial internal combustion engines to improve fuel consumption at steady loads, yet provide sufficient throttle pressure reserve for satisfactory load acceptance when the load on the engine is fluctuating.